The present invention relates to a method for preparing powder of a vinyl chloride polymer and more particularly to a method for preparing polymer powder by polymerizing, in an aqueous medium, vinyl chloride monomer or a vinyl monomer mixture principally comprising vinyl chloride monomer.
Vinyl chloride polymers have been prepared by polymerizing vinyl chloride monomer or a vinyl monomer mixture mainly comprising vinyl chloride monomer in an aqueous medium containing additives such as a suspending agent and a polymerization initiator and then dehydrating and drying the resulting polymer. However, the powder of the polymer thus obtained is liable to be electrically charged during drying or transporting the same, which in turn leads to the reduction of flow properties; hence the formation of blocks and the occurrence of clogging of the drying machine and the transport pipes. Moreover, the electrically charged polymer powder causes substantial reduction in the bulk density and, for this reason, the electrification of polymer powder easily leads to weighing error upon, for instance, volumetrically weighing the polymer powder. These phenomena become more conspicuous in the winter season during which both the temperature and humidity are low.
There have been proposed a variety of methods for preventing the electrification of powdery polymer and most of such methods generally comprise adding, to the powder of vinyl chloride polymers, a surfactant such as a nonionic surfactant, an anionic surfactant and/or a cationic surfactant to thus impart water retention characteristics to the surface of the polymer powder. However, the foregoing methods cannot sufficiently prevent the reduction in the bulk density and the lowering of the flow properties and, on the contrary, they suffer from another problem in that the thermal stability of the resulting product is sometimes impaired.
In addition to the foregoing problems, these conventional methods further suffer from the problem of adhesion of polymer scale onto the inner wall of the polymerizer.